Digital Light Processing (DLP) has been well developed and applied in digital projectors. Recently, the digital projector has shown a high potential to share traditional liquid crystal projector market; meanwhile, the key element, the so-called color wheel for carrying a set of color filters has played an important role in determining the quality of the projector. For instance, while the color wheel rotates in an extremely high speed, any rotational unbalance which occurs shall generate a high frequency noise, which would damage the manufacturer's goodwill. Therefore, improving the rotational balance of the color wheel in a better assembly process would be highly desirable in the art. Even a small breakthrough in structure or method would be helpful for the company's potential in market competition and reputation, by allowing no defect therein.
For structural concepts, design limitations and material choice to manufacture a color wheel, the readers may refer to U.S. Pat. Nos. 5,868,482 and 6,024,453 which is not repeated. However, the present invention would focus on how to assemble a color wheel to get a perfect rotational balance, which has not been taught in the related patents.
Currently, there are two major traditional methods for balancing a color wheel. Referring to FIG. 1, the first method is to bond a weight (22) to the ring (21) after the color wheel is connected to a driving motor (10). Referring to FIG. 2, the second method is to remove weight by forming a recess (23) on the ring (21). For the first method, due to the weight (22) protruding from the surface unexpected wind noise may arise. For the second method, we found that it is difficult to precisely remove the weight to reach a perfect rotational balance on the ring (21).
As shown in FIG. 3, the invention disclosed in US Patent Publication No. 2003/0035218 A1, has a ring (21) of color filter (20) with an annular groove (24) on the face which is opposite to the side of motor (10). The function of the annular groove (24) is to add weight (25) to reach a rotational balance.
There are several factors could led to the rotational unbalance of a color wheel. For instance, most of the shafts (31) of driving motors are naturally unbalanced in rotation, or the color filter which may also not be bonded in perfect position, or the thickness of adhesive layer may be unevenly formed under the color filters. These are all variable factors to the quality of the color wheel. Therefore, the known methods for balancing a color wheel include adjusting the balance after the color wheel is assembled with driving motor. As shown in FIG. 1 to FIG. 3, the color wheels easily show defects. In a worse case, a wind cut noise may also be generated.